Current-rectifying device



Patented June 24, 1930 UNETED STATES WALTER O. SNELLING, F ALLENTOWN, PENNSYLVANIA CURRENT-RECTIFYING DEVICE No Drawing.

My invention relates to current rectifying devices of the general nature of natural crystal detectors, and more particularly relates to improvements in contact rectifiers,

electric valves, contact detectors, and like devices having the property of detecting radiant energy, and of modifying and amplifying the currents set up by ether waves or vibrations.

In my pending application Ser. No. 615,160, filed January 26, 1928 and my abandoned application Ser. No. 617,173 filed February 5, 1923, of which the present application is a continuation in part, I have described the preparation of contact ele ments produced by the reaction of an element of the sulfur group and the oxide of a metal, these contact elements having no macroscopic openings or vesicles, but being characterized by the presence of extremely minute openings or pores. By the methods described in my applications already referred to both the composition and the degree of porosity of myproducts may be varied within very wide limits, and products made in accordance with my invention have been found to have important and very valuable properties in the detection and modification of electric currents set up as the result of the action of radiant energy.

I have now discovered that in addition to the methods already described in my prior application, there are other means of producing microscopically porous products having the general nature and characteristics of the contact elements which I have previously described.

As one example of my present invention I will now describe a method that I may use in the preparation of a compressed tablet possessing desirable properties as a current rectifying agent, and useful as a radio detector and for other purposes. A mixture of 80 parts of commercial white lead and 20 parts of flowers of sulful is first prepared by the careful incorporation of the two constituents in the proportions stated; The mixture is then compressed into aggregates of 5;, any desired siale or shape; preferably by Application filed. September 20, 1928. Serial No. 307,346.

means of a pellet press or tablet press, the compression being at least suflicient to give aggregates ofsuch coherence that they can be handled readily without crumbling, and preferably being in excess of 100 kilos per square centimeter. The tablets thus prepared are next heated, preferably in the absence of air, to a dull red heat. As gases are produced within the tablets by the reac; tion of their constituent materials during the period of heating, it is desirable that the heating should be conducted gently, to avoid the disruption of the tablets from the pressure of internally produced gases. A heating period of from 1 to 2 minutes at a dull red heat is satisfactory. Although neither commercial white lead nor sulfur show any current rectifying ability, the product of their reaction obtained by the process above described shows high current rectifying ability, and is useful as a detector of radio waves in both simple and reflex circuits.

Although I have referred specifically to the use of lead carbonate, either as the pure carbonate or the mixture of lead carbonate and lead hydroxide that is known as commercial white lead, as one of my preferred raw materials, my invention is not strictly limited to the use of this material, as I have found that other oxygen-containing salts of lead such as lead sulfite and lead thiosulfite may be similarly employed, the essential element of my invention being the dry reduction of an oxygen-containing salt of lead by means of an element of the sulfur group at a temperature above 400 (1., but below 1200 C. I prefer to employ a temperature of 650 0., corresponding to what is termed a dull red heat, and to employ a treating period of from 1 to 7 minutes. When a temperature in excess of 700 C. is used, I prefer to shorten my treating period some what, and when a temperature below 500 C. is employed, I find it desirable to materially lengthen the treating period beyond the maximum period of 7 minutes which gives the best results when used Within the pre= ferred temperature range.

Although I obtain the best results by the use of sulfur as the reducing agent which I employ in the dry reduction of my oxygencontaining salt of lead, my invention is not simply limited to the employment of sulfur and I recognize selenium and tellurium as the equivalents of the sulfur as reducing agents.

The products made in accordance with my invention are characterized by possessing a porous structure and are not in any way slag-like or glassy, but instead consist of a macroscopically homogeneous but microscopically heterogeneous structure made up of very minute contacting particles containing metal, oxygen and an element of the sulfur group. The presence of oxygen in my compounds is important, and it is usually of advantage to avoid so complete reduction of the lead salt or equivalent used in my products as to bring the oxygen content of the finished product to too low a figure.

Until my discovery of these new products the cause of sensitive spots in contact rectifying elements was unknown, but by my present invention I am able to control the sensitiveness of detectors of radiant energy within wide limits by suitable modifications of the atomic arrangement of my products,

the presence of dissolved but probably chemically uncombined metallic oxide and dissolved but probably chemically uncombined non-metallic element having the efiect of permitting certain ions to possess a wide freedom of movement within the chemical structure of my products. Although I do not have sufficient evidence to prove the correctness of my present theory, it is my belief that the extraordinary activity of my present products is due to the presence of dissolved oxide compounds and of a dissolved element of the sulfur group in my new compounds,

these free or dissolved components so modifying the intermolecular ionic net work which makes up the chemical compound as to leave certain ions free to enter into weak combination with one or more of the chemieal agents present. When an electric current passes through my new products the conductivity is aided by the degree of looseness with which these ions are held by the attraction of the dissolved non-metallic element and metal oxide contained in my new compound.

In most of my products a metallic sulfide, selenide or telluride forms the basic product whose ionic structural net work forms the skeleton of the molecular structure of the material, while a greater or less quantity of metallic oxide and free non-metallic element provides the source of free or mobile ions. Accordingly in order to obtain maximum sensitiveness in my products, I find it desirable to avoid such long continued reduction of my oxygen containing component, or such extensive oxidation of my non-metallic component, as will cause the complete elimination of these materials. By fusing products made in accordance with my invention their sensitiveness at once decreases to approximately the normal sensitiveness of the ordinary compound, and the distinctive properties which make my products so desirable become partly or wholly lost.

The use of increased pressure, in the operation of making tablets or pellets in accordance with my present invention, leads to increased density of the finished product in all cases. Electrical conductivity is somewhat increased and detecting ability is materially increased by the use of sufficient pressure to give a relatively high density to the finished product. It will be evident that in view of the wide variation in the-control of conditions which is possible in the practice of my present invention it is not desirable to state any specific figures for the characteristics of my products, but it is interesting to know that although the specific gravity of lead sulfide as the mineral galena varies from 7 .4 to 7.6, the corresponding product made in accordance with my invention by the reaction of an oxygen-containing compound of lead and sulfur has a specific gravity ranging normally from 2.0 to 5.0, according to the composition of the primary base mix and the degree of pressure used in forming tablets of the material. In considering the above figures, it is to be remembered that my compound is not pure lead sulfide, however, but

that in addition to lead sulfide it also contains oxygen compounds of lead, and also some free or loosely combined sulfur, and accordingly a strict comparison of its specific gravity with the specific gravity of galena is not fair. In general, however, products made in accordance with my invention are less dense than the corresponding minerals which contain the metal and the element of the sulfur group predominating in my product. In appearance my products are usually smooth, hard blocks, varying in color according to their composition, and even when the surfaces are polished are not glassy or slag-like. My products show no visible openings except on magnification, and are tough and very slightly elastic.

It will be evident that many modifications may be made without departing from the spirit of my invention as disclosed. Although I have illustrated my invention by certain specific embodiments, my invention is such as are indicated in the appended claims.

I claim:

1. The process of preparing current rectifying products which comprises reducing a substantially dry salt of lead by an element of the sulfur group.

2. The process of preparing current rectifying products which comprlses reducing a substantially dry carbonate of lead by an element of the sulfur group.

3. The process of preparing current rectifying products Which comprises reducing a substantially dry basic lead carbonate by an element of the sulfur group.

In testimony whereof, I have hereunto subscribed my name this 18th day of September, 1928.

WALTER O. SNELLING. 

